Method and apparatus for detecting spoilage

ABSTRACT

System for non-destructive detection of spoilage in sealed containers of food or other perishable commodities. The invention utilizes the principle that growth of spoilage organisms is accompanied by an evolution of heat.

United States Patent Sacks et a1.

[ Nov. 13, 1973 [5 METHOD AND APPARATUS FOR 2,975,629 3/1961 Herbert73/15 B DETECTING SPOILAGE 3,699,813 10/1972 Lamb 73/342 [75] Inventors:Lawrence E. Sacks, Berkeley;

Emory Menefee, Richmond both of FOREIGN PATENTS OR APPLICATIONS Calif452,922 5/1968 Switzerland 73/340 [73] Assignee: The United States ofAmerica as represented by the Secretary of Primary Examiner-Richard C.Queisser Agriculture, Washington, DC. Assistant ExaminerJoseph W. Roskos[22] Filed: y 1972 Att0rneyR. Hoffman et al.

[21] Appl. No.: 270,426

[57] ABSTRACT [52] US. Cl. 73/52, 73/340 [51] Int. Cl. ..G01n 25/48System for nondestructive detection f spoilage in Fleld of Search ealedcontainers of food or other perishable com- 73/342, 15 B modities. Theinvention utilizes the principle that growth of spoilage organisms isaccompanied by an [56] References Cited evolution f a UNITED STATESPATENTS 2,512,134 6/1950 Baule 73/52 X 6 Claims, 4 Drawing Figures W 4 A4 B 4 C 4 D 4 E PATENTEmmv 13 1915 SHEET 10F 2 mgr/2V AV A A! sA saRecorder quenTiol Sw|tch Time METHOD AND APPARATUS FOR DETECTINGSPOILAGE A non-exclusive, irrevocable, royalty-free license in theinvention herein described, throughout the world for all purposes of theUS. Government, with the power to grant sublicenses for such purposes,is hereby granted to the Government of the United States of America.

DESCRIPTION OF THE INVENTION This invention relates to and has among itsobjects the provision of novel method and apparatus for detectingspoilage in sealed containers of food or other perishable commodities.

Further objects of the invention will be evident from the followingdescription and the annexed drawing.

In the drawing:

FIGS. 1 and 2 are schematic diagrams of apparatus in accordance with theinvention.

FIG. 3 depicts a position of a chart displaying results yielded by theapparatus of the invention.

FIG. 4 is a diagram illustrating the operation of the sequential switch.7

In the following description, emphasis will be directed to foodproducts. It is to be understood, however, that the invention is notrestricted to foods, but is applicable to all kinds of perishablecommodities such as vitamins and vitamin precursors; feeds; medicinalpreparations; cosmetics; glues; pastes, latices; starches and proteins(industrial as well as food or feed grades), etc.

Canning is a universally used method of preserving foods. It involvessealing the food in containers-usually metal cans or glass jarsand thenheating the sealed containers to destroy the microflora in the food andassociated with the containers themselves.

It can be readily visualized that if the sealed containers are subjectedto a very rigorous heating operation one can be assured that no viablemicro-organisms will remain in the products, and no danger of spoilagewill be encountered when the products are stored (assuming, of course,that the containers remain hermetically sealed).

However, there is another aspect to be considered and that is thequality of the preserved foodfor example, its taste, texture,nutritional value, and color. These attributes, in turn, are dependenton the degree to which the food is heated and if the heating conditionsare excessive, the quality of the food will be so low that the productwill not be marketable.

In actual practice, therefore, the manufacturer must strike a balancebetween the opposing factors outlined above. His heating operation mustbe adjusted to such a level as to maintain the quality of the food, yetto achieve such degree of microbial destruction that the product willnot spoil. The maintaining of this balance in day-to-day operations in acannery is difficult, and at times some of the canned products willspoil. To prevent spoiled products from reaching the market, it hasbecome conventional for canners to use the following technique: Afterthe cans have been heat processed (or retorted, as this step is oftentermed) the cans are cooled and then stored at ambient temperature for aperiod of time. This storage provides, as it were, an opportunity forspoilage to develop in those cans which have not received adequate heatprocessing. When the storage period is up, the individual cans areexamined for swelling (gas formation). This may be done visually, or,more accurately, by mechanical devices which test residual vacuum in thecans by the amount of tension required to flex the can ends. The canswhich pass this inspection are forwarded to the usual marketingchannels; those which show gas formation are destroyed.

Most spoilage micro-organisms are gas producers and therefore theabove-outlined scheme of storage and inspection prior to marketing is ofgreat benefit in preventing spoiled products from reaching the market.However, a few organisms (Bacillus coagulans and Bacillusstearothermophilus, for example) are not gas producers and therefore ifthe product should contain viable forms of such organisms, theirpresence cannot be detected by tests for gas formation. The type ofspoilage in question is generally termed flat souring" because the canends remain flat, i.e., not bulged as they would be by ubiquitousgas-producing organisms. It is evident from the foregoing that even withthe application of storage and inspection, there may be instances ofundetected spoilage. v I

A primary object of the invention is the provision of means wherebyspoilage within sealed containers can be detected regardless of whetherthe spoilage is caused by gas-producing organisms, flat souringorganisms, or combinations thereof.

Another object of the invention is the provision of a system forspoilage detection which obviates handling of the containers and visualinspection thereof in that the indicia of product quality is displayedat any convenient location such as one remote from the containers.

A further object of the invention is the provision of means wherebyspoilage in sealed containers can be detected at the time the spoilageoccurs.

The invention utilizes the principle that growth of an organism isaccompanied by an evolution of heat. Although this basic principle isknown, it has never to our knowledge been applied for detecting spoilagewithin a sealed container, and, moreover, the bare knowledge of thisprinciple cannot be used in any practical way for such detection. Thisis further explained as follows: One item to be considered is that thetemperature developed by growing micro-organisms is measurable butminute, amounting to a few hundredths or at most a tenth ofa degree, C.Because such a small temperature rise is involved, it cannot bedifferentiated from temperature variations caused by other factors. Forexample, if a can of food is held in an ordinary storage area andsubjected to temperature measurements over a period of time, it will befound that the temperature will vary widely over several degrees causedby such factors as weather conditions, the usual diurnal temperaturecycle, changes in air currents caused by movement of persons, doors,machinery, etc. Since these extraneous factors cause temperaturevariations far in excess of any which might be due to microbial growth,the procedure does not provide any indication of the quality of the foodwithin the can.

In accordance with the invention the difficulty outlined above isobviated by a system which balances out extraneous temperaturevariations, that is, variations due to causes other than microbialgrowth. As a result, the quality of the food within the container can beassessed for spoilage even though the can is subjected to temperaturevariation by extraneous causes. Another advantage of the invention isthat it is nondestructivethe detection is made without damaging oraltering the product in any way. One manner by which such desirableresults are obtained is next described in detail, having reference tothe annexed drawing.

FIG. 1 represents a portion of a storage area wherein cans ofaparticular food are held after they have undergone the usual heatprocessing and cooling steps. In this area, the cans are held for aperiod of time to permit development of spoilage in those cans which mayhave inadvertently received inadequate heat processing or have pinholesor other defects of sealing.

Numeral l designates a representative support on the storage area, thissupport being preferably fabricated from a material which is aninsulator (both electrical and thermal).

Support 1 is provided with circular recesses 3 for positioning cans 4filled with a particular food. To differentiate individual cans they aredesignated 4A, 4B, 4C, etc.

Within support 1 is mounted a series of temperature sensors 5, theindividual units being designated 5A, 5B, etc. These sensors may takethe form, for example, of thermistors or thermocouples.

When cans 4 are in position on support 1, each sensor 5 contacts one ofthe cans (for example, sensor 5A with can 4A, sensor 58 with can 4B,etc.) and provides an electrical signal representative of thetemperature of the can with which it is in registration.

Each of the sensors 5 is connected with appropriate lead wires(collectively designated by numeral 6) for conducting the electricalsignals provided thereby. These leads are threaded through conduit 2whereby to establish communication with a signal-processing meanshereinafter described.

FIG. 2 depicts a signal processing and displaying means which includessequential switch 7 and recorder 8.

The heads 6 from sensors 5 provide an input of primary signals tosequential switch 7. In the following explanation, the respectivesignals from sensors 5A, 5B, 5C, etc., are hereinafter designated as A,B, C, etc.

Within switch 7 the incoming primary signals A, B, C etc., are processedas follows: At fixed intervals of time (for example, every hour) a pairof signals from adjacent cans are composited to form a secondary signalrepresenting the difference between the primary signals so that thissecondary signal represents the difference in temperature betweenadjacent cans. For example, at the first point of time signals A and Bare composited to form a secondary signal A minus B, at the second pointof time signals C and D are composited to form a secondary signal Cminus D, and so on over and over again during the storage period. Switch7 also operates to sequentially direct the secondary signals to recorder8 where these are displayed, as by a dot on a recording chart 9. Theaforesaid action is repeated as each pair of individual primary signalsare composited. For example, at the first point of time the secondarysignal A minus B is displayed, at the next point of time secondarysignal C minus D is displayed, and so on over and over again during theperiod of storage. It is obvious that the displays of individual signalsA minus B, C minus D, etc. need to be presented on chart 9 in such amanner--as by utilizing different portions of the chart-that the traceseventually yielded by each can be distinguished from the others. Thetraces or curves representing the secondary signals have thesignifiwhere the secondary signals stay at zero the cans in the pairhave no relative temperature difference, hence there is no spoilage.Where, however, the chart shows a positive or negative value, it meansthat one of the cans in the pair is warmer than the other-i.e.,microbial growth is taking place within one of the cans in the pair.This item is further explained below in connection with FIG. 3 whichdepicts a portion of recording chart 9. In this figure, the units shownfor temperature and time are arbitrary.

Trace 10 represents the secondary signal A minus B. Since the traceindicates a continuous relative temperature of zero, it signifies thatno microbial growth is taking place in either can 4A or 4B.

Trace 11 represents the secondary signal C minus D. In this case therelative temperature remained constant at zero for a time and then roseto a peak at about the 15th unit of time. This means that that can, 4C,was warmer than can 4D, i.e., microbial growth occurred in can 4C. Tosum up the results: Cans 4A, 4B, and 4D are free from spoilage and can4C is spoiled and is to be discarded.

FIG. 4 illustrates a form of electrical arrangement to provide thedesired compositing of primary signals. This figure is framentary inthat it includes only a portion of the apparatus, the arrangement of theremainder will be obvious from that which is shown.

Sensors 5A, 58, etc. which take the form of conventional thermo-couplesare connected in series in constantan-to-constantan andcopp'er-to-copper relationship. This is indicated in the figure by theabbreviations Con and Cu.

Within sequential switch 7 (represented by the broken lines) are a pairof ganged switches 15A, 15B, and a similar pair 15C, 15D. These arenormally in open position, and at predetermined intevals one or theother pair is closed by conventional means not illustrated. For example,at a first point of time switches 15A and 15B are closed. Therebysensors 5A and 5B are connected to terminals 16 and'l7 which, in turn,are connected to recorder 8. Since sensors SAand -5B are joined in suchmanner that the developed EMFs oppose one another, the primary signals Aand B are subtracted one from the other, and the resulting secondarysignal which is representative of the relative temperature between cans4A and 4B is impressed across terminals l6 and 17. In a second point oftime, switches 15C and 15D are closed whereby a corresponding actiontakes place, and a secondary signal representative of the relativetemperature between cans 4C and 4D is impressed across terminals 16 and17. In similar manner, secondary signals representative of relativetemperatures between all adjacent cans in the system are periodicallyimpressed across terminals 16 and 17 and so displayed by recorder 8.

As explained above, a critical feature of the invention is that it makespossible the selective detection of temperature changes attributable tomicrobial growth. Such a desirable result is primarily due to thefeature that we measure relative temperatures (in contrast to absolutetemperatures), whereby the effects of extraneous factors areneutralized. This item can be demonstrated as follows: If two cans areplaced in a conventional storage room, their temperature will fluctuateconsiderably due to extraneous factors such as the diurnal temperaturecycle. Accordingly, the temperatures of the individual cans cannotpossibly give any clue to microbial growth which may be taking placewithin the cans. On the other hand, where one measures the relativetemperature between the two cans, the extraneous temperature changesbeing the same as to each can are canceled out so that any residualamount reflects microbial activity within one or the other of the cans.

To obtain optimum neutralization of extraneous temperature changes, weprefer to apply our relative measurements to sets of can wherein theindividual cans of each set are near one another. The significance ofthis is that if there are localized temperature variations within thestorage area, the cans which are in proximity to one another will beaffected equally. This, in turn, means that the extraneous factors willcompletely neutralize one another in the relative temperaturedetermination.

Also for best results it is preferred that individual cans of each setbe of the same size, and contain the same amount of the same product. Inthis way one can be assured that any factors (extraneous or due tomicrobial growth) will affect the temperature of individual cans to thesame extent. For example, equal-sized cans of the same food product willhave equal thermal properties, such as heat capacity. Therefore, if theyare exposed to a temperature-affecting condition, they will both beaffected to the same degree.

In the preceding illustration, it is explained that display ofa positiveor negative relative temperature is an indication of spoilage in one orthe other of the set of cans. There should also be considered the pointthat both cans in a set might contain spoilage organisms. In such case,there might be a display of zero relative temperature-that is, a falseindication of good quality. However, there are several factors whichmilitate against such a possibility. A zero relative temperature wouldbe displayed only in the unlikely event that both cans would spoil atthe same time and to the same extent. If both cans should containspoilage organisms, the odds are greater that there would be differencesin time of spoilage and degree of spoilage with the result that apositive or negative relative temperature would be registered.Accordingly, the presence of spoilage would be detected. Moreover, thepossibility of a false indication could be decreased by placing cans inthe apparatus in such sequence that adjacent cans would not be from thesame heat-processing bath. Although processors always aim at uniformheat processing, there are always minor variations in such factors astemperature and time of heating from batch to batch. Accordingly, if thecans are positioned in the manner described above, one will greatlydecrease the likelihood that adjacent cans will both contain spoilageorganisms and even more decrease the likelihood that both will containthe same organism in the same amount. Another technique for minimizingfalse indications involves the inclusion of a reference can within eachset of cans. By reference can we mean a can of the same product butwhich had been treated in such a way as to preclude all possibility thatit could spoil. This could be arranged by adding a bactericide to thecontents and/or by deliberately over-processing it. This can would, ofcourse, not be intended for use other than as a reference and would bemarked accordingly to prevent its being co-mingled with the other canson completion of the storage period. After one period of storage anddetection is completed,-the reference cans could be kept in place foruse in connection with the next lot of cans to be assayed for spoilage.By using reference cans in this way, one is assured that if a positiveor negative relative temperature is displayed by any particular set, thespoilage is not in the reference can but in the other can of the set.

It will be understood that the embodiment of the invention described indetail above may be modified in many ways, and that such modificationsare included in the broad ambit of the invention. Several modificationsare listed below by way of illustration and not limitation.

Generally, the cans undergoing detection for spoilage are held in anarea of ordinary (room) temperature since if there are spoilageorganisms present they will multiply at such temperatures, hence providethe desired indication of their presence. If, however, it is desirkd toaccelerate the process, the cans may be held at somwhat elevatedtemperature to enhance microbial growth. Thus, for example, the storagemay. be in rooms maintained at temperatures as high as about C. Insituations where there is a possiblity of spoilage due to severalorganisms having different temperature-growth patterns, the can may bestored for a period of one temperature level which is optimum for growthof one of the suspected organisms and then stored for another period ata temperature which is optimum for growth of another of the suspectedorganisms. From the foregoing, it is evident that in any case tbe cansare to be stored at temperatures conducive to microbial growth and thatthis, in general, will be from about 20 to about C.

The temperature measurements for spoilage detection may be conductedwith any kind of instrumentality which is capable of sensing smalltemperature changes. Thus instead of thermistors, one could employthermocouples or other contact devices which sense temperature bycausing electrical changes. Optical devices could also be used, in whichcase contact would not be required. Such instruments have a lens andphoto cell arrangement and measure the heat radiated by an ob ject. Forthe purposes of the invention such'an optical device would be arrangedto scan a band of cans at fixed intervals and transfer the signals to asignal pro-- cessing means as heretofore described. There are on themarket paints which have the ability to change color as the temperatureof the object on which they are coated varies. Such a paint could beapplied mutt; cans and an optical device such as a photometer used toaccurately measure the color of the 'paint coating" and thereby providesignals as to the temperatures of the cans. Also suitable for thepractice of the invention are infrared pyrometers, bolometers, orinfraredsensitive video camera equipment. For example, there areavailable on the market infrared scanning devices which can accuratelydetect temperatures by measuring the infrared radiation given off byobjects. Devices- I being then displayed on anoscilloscope or similarviewing screen.

In the modification detailed above each set contains two individualcans. It will be obvious that this is not a critical item. The sets maycontain more than two cans, in which case the signal processing meanswould be adjusted to detect the relative temperature of the cans in eachset of three, four, or more cans. Where such larger sets are used itwould be preferable-if a positive or negative relative temperature isdisplayed-to discard all the cans of the set rather than trying toisolate the individual can which is contaminated.

In the detailed modification the detection results are displayed aspoints on a chart, these points eventually forming traces or curves.This system of displaying the information is not critical and one mayemploy various other systems. For example, a digital printer may be usedto display the values of the secondary signals in numeral form fordirect viewing or they may be recorded on tapes, discs, or the like. Therecorded information may then be fed into a computer programmed to scanthe information obtained during the entire storage period and provide areadout indicating which sets of cans exhibited microbial activityduring the period of storage.

Further modifications of the invention will, of course, be obvious tothose skilled in the art from the foregoing illustrations.

EXAMPLE The invention is further demonstrated by the followingillustrative example.

Two cans of corn which had been subjected to conventional heatprocessing were treated as follows:

One can was punctured and inoculated with Bacillus macerans. Nothing wasdone to the other can.

A thermocuple was taped to an end of each can, the leads from thethermocouples being connected with a recorder through a differentialamplifier to determine the relative temperature of the cans from time totime while they were stored at ambient temperatures, and to display thisinformation.

The results obtained are tabulated below:

Time, hrs. Relative temp., C. 0.000 0.000 0.042 0.060 0.084 0.096 0.0960.080 0.060 0.018 0.006 70 0.000

Having thus described the invention, what is claimed is:

1. A method for non-destructive detection of spoilage in sealedcontainers enclosing a perishable commodity, which comprises:

a. storing the containers at a temperature conducive to microbialgrowth, with individual containers in close proximity to one another.

b. during said storage period taking primary measurements of thetemperatures of individual containers as influenced by both extraneousand internal factors, and

c. converting the primary temperature measurements of adjicentindividual containers into secondary measurements providing an index tothe quality of the containers and their enclosed contents. 5 2. A methodfor non-destructive detection of spoilage in sealed containers enclosinga perishable commodity, which comprises:

a. storing the containers at a temperature conducive to microbialgrowth, with individual containers in close proximity to one another,

b. during the storage providing primary signals representative of thetemperatures of individual containers as influenced by both extraneousand internal factors,

c. processing the primary signals from adjacent individual containers toeliminate components derived from extraneous temperature factors and toprovide secondary signals representative solely of internal temperaturefactors, and,

d. displaying said secondary signals to provide an index to the qualityof the containers and their enclosed contents.

3. Apparatus for non-destructive detection of spoilage in sealedcontainers enclosing a perishable commodity, which comprises a. meansfor storing said sealed containers, with individual containers in closeproximity to one another,

b. temperature-sensing means for providing primary signalsrepresentative of the absolute temperatures of individual containers,

c. signal-processing means coupled with said temperature-sensing meansand programmed to receive the primary signals from adjacent individualcontainers and to convert them into secondary signals representative ofthe relative temperature of sets of the containers, and

d. means for displaying said secondary signals to provide an index ofthe quality of the containers and their enclosed contents.

4. Apparatus for non-destructive detection of spoilage in sealedcontainers enclosing a perishable commodity, which comprises a. meansfor supporting the containers in an area maintained at a temperatureconducive to microbial growth, with individual containers in closeproximity to one another,

b. temperature-sensing means for providing primary signalsrepresentative of the absolute temperatures of individual containers,

c. signal-processing means coupled with the said temperature-sensingmeans and programmed to receive said primary signals from adjacentindividual containers, and to convert them into secondary signalsrepresentative of the relative temperature of selected sets ofcontainers, and

d. means for displaying said secondary signals to provide an index ofthe quality of the containers and their enclosed contents.

5. Apparatus for non-destructive detection of spoilage in sealedcontainers enclosing a perishable commodity which comprises a. means forstoring said sealed containers, with individual containers in closeproximity to one another,

b. a plurality of temperature-sensing elements, each element inoperative relationship with a single container for producing a primarysignal representative of the absolute temperature of individualcontainers it is associated with,

c. signal processing means coupled with said temperature-sensingelements and programmed to receive said primary signals from adjacentindividual containers and to convert them into secondary signalsrepresentative of the relative temperatures of selected sets ofcontainers, and

d. means for displaying said secondary signals to provide an index ofthe quality of thecontainers and their enclosed contents.

6. Apparatus for non-destructive detection of spoilage in sealedcontainers enclosing a perishable commodity, which comprises a. meansfor supporting the containers in an area maintained at a temperatureconducive to microbial growth, with individual containers in closeproximity to one another,

b. a plurality of temperature-sensing elements, each in operativerelationship with a single container for producing a primary signalrepresentative of the absolute temperature of the container it isassociated with,

c. signal-processing means coupled with said temperature-sensingelements and programmed to sequentially receive primary signals derivedfrom selected sets of the containers, to eliminate from these primarysignals components derived from extraneous temperature variations, andto sequentially convert the primary signals into secondary signalsrepresentative of temperature variation within the containers, and

(1. means for displaying said secondary signals to provide an index tothe quality of the containers and their enclosed contents.

1. A method for non-destructive detection of spoilage in sealedcontainers enclosing a perishable commodity, which comprises: a. storingthe containers at a temperature conducive to microbial growth, withindividual containers in close proximity to one another. b. during saidstorage period taking primary measurements of the temperatures ofindividual containers as influenced by both extraneous and internalfactors, and c. converting the primary temperature measurements ofadjicent individual containers into secondary measurements providing anindex to the quality of the containers and their enclosed contents.
 2. Amethod for non-destructive detection of spoilage in sealed containersenclosing a perishable commodity, which comprises: a. storing thecontainers at a temperature conducive to microbial growth, withindividual containers in close proximity to one another, b. during thestorage providing primary signals representative of the temperatures ofindividual containers as influenced by both extraneous and internalfactors, c. processing the primary signals from adjacent individualcontainers to eliminate components derived from extraneous temperaturefactors and to provide secondary signals representative solely ofinternal temperature factors, and, d. displaying said secondary signalsto provide an index to the quality of the containers and their enclosedcontents.
 3. Apparatus for non-destructive detection of spoilage insealed containers enclosing a perishable commodity, which comprises a.means for storing said sealed containers, with individual containers inclose proximity to one another, b. temperature-sensing means forproviding primary signals representative of the absolute temperatures ofindividual containers, c. signal-processing means coupled with saidtemperature-sensing means and programmed to receive the primary signalsfrom adjacent individual containers and to convert them into secondarysignals representative of the relative temperature of sets of thecontainers, and d. means for displaying said secondary signals toprovide an index of the quality of the containers and their enclosedcontents.
 4. Apparatus for non-destructive detection of spoilage insealed containers enclosing a perishable commodity, which comprises a.means for supporting the containers in an area maintained at atemperature conducive to microbial growth, with individual containers inclose proximity to one another, b. temperature-sensing means forproviding primary signals representative of the absolute temperatures ofindividual containers, c. signal-processing means coupled with the saidtemperature-sensing means and programmed to receive said primary signalsfrom adjacent individual containers, and to convert them into secondarysignals representative of the relative temperature of selected sets ofcontainers, and d. means for displaying said secondary signals toprovide an index of the quality of the containers and their enclosedcontents.
 5. Apparatus for non-destructive detection of spoilage insealed containers enclosing a perishable commodity which comprises a.means for storing said sealed containers, with individual containers inclose proximity to one another, b. a plurality of temperature-sensingelements, each element in operative relationship with a single containerfor producing a primary signal representative of the absolutetemperature of individual containers it is associated with, c. signalprocessing means coupled with said temperature-sensing elements andprogrammed to receive said primary signals from adjacent individualcontainers and to convert them into secondary signals representative ofthe relative temperatures of selected sets of containers, and d. meansfor displaying said secondary signals to provide an index of the qualityof the containers and their enclosed contents.
 6. Apparatus fornon-destructive detection of spoilage in sealed containers enclosing aperishable commodity, which comprises a. means for supporting thecontainers in an area maintained at a temperature conducive to microbialgrowth, with individual containers in close proximity to one another, b.a plurality of temperature-sensing elements, each in operativerelationship with a single container for producing a primary signalrepresentative of the absolute temperature of the container it isassociated with, c. signal-processing means coupled with saidtemperature-sensing elements and programmed to sequentially receiveprimary signals derived from selected sets of the containers, toeliminate from these primary signals components derived from extraneoustemperature variations, and to sequentially convert the primary signalsinto secondary signals representative of temperature variation withinthe containers, and d. means for displaying said secondary signals toprovide an index to the quality of the containers and their enclosedcontents.